This invention relates generally to a method for connecting the terminal posts of a connector to a substrate, such as a printed circuit board, and more particularly it relates to a method of soldering said connector terminal posts to a plated through hole of a printed circuit board.
Connectors having a plurality of terminal posts which fit through holes in printed circuit boards are in extensive use today and have many different applications. One such application is, for example, the connection of one circuit board to another circuit board. A connector for this purpose usually consists of a row of pairs of contacts aligned so that the spacing between the contacts forms a slot which can receive the edge of a first printed circuit board. The other ends of the contacts are formed into terminal posts which are intended to extend through holes in a second printed circuit board. A plastic housing is usually provided to hold the pairs of contacts in a fixed position with respect to each other and for insulative purposes. In this type connector the posts usually consists of a plurality of pairs of posts which form two rows of posts. The terminal posts of the connector are pushed or pulled through the holes in the second printed circuit board and often are soldered into place. However, the percentage of acceptable soldered connections between the posts and the printed circuit board is not always as high as desired. It is desirable that the solder flow in and around the post and completely through the hole. In other words, the solder should completely fill up the hole around the posts. One widely used method of soldering such posts to printed circuit boards is by wave soldering wherein the bottom of the printed circuit board with the terminal post extending therethrough is positioned just below the surface of a pool of hot solder which is pulled up into the spaces between the posts and the sidewalls of the hole in the printed circuit board by such phenomena as surface tension or capillary action, or a combination of both. Often times, however, the solder does not rise sufficiently far up into the hole of the printed circuit, leaving a comparatively weak solder joint with a high probability of failure under stress at a later date when in actual use.
Another technique is to insert the terminal post through the hole of the printed circuit board and then place a solder doughnut (i.e., a torus shaped piece of solder) around each terminal post where it extends through the printed circuit board. The solder toruses are then melted by suitable heating means and flows into the hole in and around the terminal post. However, the problem of individually placing solder doughnuts on each of the terminal posts after they have been inserted through their mating hole in the printed circuit board is a time-consuming one and quite expensive.